The present invention relates to new derivatives of hydrazinium phosphites, their preparation and the fungicidal compositions in which at least one of these compounds is present as the active material. Hydrazinium phosphites are sometimes called hydrazinium phosphonates.
More precisely, the invention relates to compounds corresponding to the formula: ##STR2## in which R.sub.1 represents a hydrogen atom, or an alkyl radical containing from 1 to 4 carbon atoms, and R.sub.2 represents a hydrogen atom, or a phenyl nucleus which is optionally substituted by one or more of the following atoms or radicals: the nitro radical, an alkyl radical (C.sub.1 -C.sub.4) and halogen, it is not possible for R.sub.1 and R.sub.2 to simultaneously represent a hydrogen atom.
It has long been known that hydrazine (or hydrazine hydrate) exhibits valuable pesticidal properties, in particular fungicidal, bactericidal and insecticidal properties. Unfortunately, both hydrazine and hydrazine hydrate exhibit extremely high phytotoxicity, which completely prohibits their use for the treatment of plants.
In order to reduce this phytotoxicity, a process of fungicidal treatment using hydrazine salts with inorganic phosphorus acids chosen from the group comprising phosphoric acid, phosphorous acid, hypophosphoric acid and pyrophosphoric acid has been proposed in U.S. Pat. No. 2,773,796. This patent describes, in particular, the use of hydrazinium phosphite against tomato mildew (Phytophthora infestans) and against septoriosis in celery (Septoria graveolentis). However, no information is given concerning the possible use of this hydrazinium phosphite for the treatment of vine mildew (Plasmopara viticola); although, from an economic point of view, it is in fact vines which constitute one of the main fields of application of anti-mildew treatments. Experiments which we have carried out on vines in a greenhouse have shown that, when applied to the foliage, hydrazinium phosphite exhibits significant phytotoxicity towards vine seedlings, and that therefore it is not possible to use it in this field.
Furthermore, the use of compositions containing, as the active material, various derivatives of phosphorous acid has been proposed for fungicidal treatments.
Thus, the use, of inorganic or organic salts of phosphorous acid, as fungicides has been claimed in French Pat. No. 2,252,056 and; in its Certificate of Addition 2,285,812, the use of salts of phosphorous acid and of imidazole, cyclohexylamine or morpholine as fungicides has been claimed.
As organic salts of phosphorous acid, these two patents describe, in particular, acid phosphites of ammonium or of ammonium which is substituted by one or more alkyl, hydroxyalkyl or phenyl groups, this group itself being optionally substituted. However, no hydrazinium phosphite is described in the examples.
Furthermore, in French Pat. No. 2,254,276 the use has been claimed, of fungicides which are phosphonic acid monoesters (also called phosphites) of the general formula: ##STR3## in which M represents a hydrogen atom, an optionally substituted ammonium cation, or a metal cation, n is an integer equal to the valency of M and R.sub.3 can represent an alkyl radical containing from 1 to 18 carbon atoms. In its Certificate of Addition U.S. Pat. No. 2,288,463 the use of, fungicides is claimed, which are compounds of the formula 2 in which M is an ammonium cation which is substituted by one or more alkyl or hydroxyalkyl radicals, n is an integer ranging from 1 to 3 and R.sub.3 can represent a C.sub.1 -C.sub.8 alkyl group. This French Pat. No. 2,254,276 and its Certificate of Addition U.S. Pat. No. 2,288,463 describe, in particular, the use of ammonium alkyl-phosphites in which the ammonium ion is substituted by one or more alkyl, hydroxyalkyl or phenyl groups. However, no hydrazinium alkyl-phosphite is mentioned in the examples.
The phosphites or alkyl-phosphites described in these French Pat. Nos. 2,252,056 and 2,254,276, and in their respective Certificates of Addition U.S. Pat. Nos. 2,285,812 and 2,288,463, exhibit remarkable fungicidal properties, especially against vine mildew, namely an immediate, preventive or curative and systemic action combined, for the majority of the compounds, with the absence of phytotoxicity in vines. However, complementary experiments carried out on vines in the open air have shown that, depending on the climatic conditions, optionally substituted ammonium alkyl-phosphites can lead to significant occurrences of phytotoxicity in the vines, and that their use in this field is therefore to be proscribed.
Because of the well known phytotoxicity of hydrazine, and because of the results already observed on vines in the case of hydrazinium phosphite described in U.S. Pat. No. 2,773,796, and in the case of the abovementioned phosphites or alkyl-phosphites of ammonium or of substituted ammonium, it could be expected that phosphites or alkyl-phosphites of hydrazinium or of substituted hydrazinium would generally exhibit high phytotoxicity, which would prohibit, in particular, their use by application to foliage.